Fast characterization of soluble organic intermediates and integrity of microbial cells in the process of alkaline anaerobic fermentation of waste activated sludge

• Fast characterization method of alkaline sludge fermentation process is proposed.
• Flow cytometry is coupled with excitation–emission matrix fluorescence spectra.
• Instant identification of dynamic change of bacterial cells with flow cytometry.
• Soluble organics products are fast characterized by excitation–emission matrix.
• Tryptophane-like fluorescence plays key role in monitoring soluble organics.

Interest in alkaline anaerobic fermentation of waste activated sludge (WAS) is on the rise recently due to its excellent result in sludge reduction and biomass reuse. However, there is still lack of ideal approaches to monitor the fermentation process. The authors present here a fast method for tracing status of microbes and soluble fluorescent organics during alkaline anaerobic fermentation by coupling flow cytometry (FCM) and three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy. FCM primarily reveals the cell integrity and identifies sources of soluble organics, while 3D-EEM further characterizes them in different fermentation phases by correlation with fluorophores such as soluble protein. High correlation was obtained between fluorescence intensities of three peaks, especially those related to tryptophan-like (Ex/Em: 280/340 nm) and main soluble organics. The proposed method significantly reduced the time by over 90% compared with conventional methods. The method demonstrates great potential for application in efficient controlling and monitoring in practical alkaline fermentation process.

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